1. Field of the Invention
This invention relates to industrial extreme pressure gear lubricants having enhanced oxidative and thermal stability.
2. Description of the Related Art
Industrial extreme pressure gear lubricants are used in practically every aspect of the manufacturing and processing industry. Industrial gear lubricants are most frequently used in such components as reduction gears, drive units, screws, slides, chains, and the like. Of the three recognized types of industrial gear lubricants, the most important are the extreme pressure or EP gear oils. In addition to protecting metal parts from corrosion and thermal and oxidative deterioration, EP gear oils must also provide protection against scoring and other types of mechanical distress. EP gear oils are based on petroleum-based or synthetic materials. The petroleum-based EP oils are usually comprised of a petroleum-based material such as mineral oil, an antioxidant, an antifoam, a corrosion inhibitor, and one or more EP additives. In synthetic gear oils, the petroleum-based material is replaced with such synthetic substances as hydrocarbons, esters, polyglycols, phosphate esters, silicones, silicate esters, polyphenyl ethers, and halogenated hydrocarbons depending upon the particular application. It is well known in the art that synthetic gear lubricants tend to last longer, exhibit better high temperature stability, have higher viscosity indexes, and usually have lower pour points than petroleum-based lubricants. Because industrial gear horsepower ratings have increased fourfold over the last 15 years, gear oils are subjected to increasingly higher temperatures which causes a correspondingly shorter service life due to thermal and oxidative degradation. Thus there is always a need for industrial EP gear oils which can provide enhanced oxidative and thermal stability. The compositions according to the invention are industrial gear lubricants having improved high temperature performance, high temperature stability, and cleanliness.
It has been discovered surprisingly that a composition which is comprised of: (a) a poly-xcex1-olefin which has a viscosity of from 4 centistokes to 100 centistokes @ 100xc2x0 C.; (b) a polyol ester made by reacting a monocarboxylic acid having from 5 to 18 carbon atoms and a polyol which has at least 3 alcohol functionalities; (c) a polybutene having a molecular weight of from about 700 to about 2500 Daltons; (d) an antioxidant; (e) a sulfur/phosphorus type extreme pressure additive having a specific gravity @ 15.6xc2x0 C. equal to 1.022; a viscosity in centistokes @ 100xc2x0 C. equal to 14.3; color according to ASTM D 1500 equal to 4.0; % boron by weight equal to 0.36; % nitrogen by weight equal to 1.21; % phosphorus by weight equal to 1.61; % sulfur by weight equal to 19.6 affords an extreme pressure industrial gear lubricant having enhanced oxidative and thermal stability, and higher viscosity index relative to petroleum-based lubricants and other polyol ester-based lubricants.
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term xe2x80x9caboutxe2x80x9d.
The poly-xcex1-olefins which can be used in the compositions according to the invention are those which have a viscosity in the range of from about 4 centistokes to about 100 centistokes @ 100xc2x0 C. Preferred poly-xcex1-olefins are those which have a viscosity in the range of from about 4 centistokes to about 10 centistokes @ 100xc2x0 C. The amount of poly-xcex1-olefin which can be used in the compositions according to the invention can range from 20% by weight to 90% by weight and will preferably be in the 25% by weight to 55% by weight range.
The polyol esters which can be used in the composition according to the invention are those which can be made by esterifying monocarboxylic acids having from 5 to 18 carbon atoms with a polyol having at least 3 alcohol functionalities examples of which include but are not limited to such polyols as neopentyl glycol (2,2-dimethyl-1,3-propanediol), trimethylolethane [2-methyl-2-(hydroxymethyl)-1,3-propanediol], trimethylolpropane [2-ethyl-2-(hydroxymethyl)-1,3-propanediol], pentaerythritol, dipentaerythritol, glycerine, diglycerine, and triglycerine. The preferred polyol esters are esters of pelargonic acid. The most preferred polyol ester according to the invention is trimethylolpropane tripelargonate. The molecular weight of the polyol esters which can be used can range from 270 to 1,900 with those having a molecular weight of from 480 to 1,400 being preferred. The amount of polyol ester which can be used in the compositions according to the invention can range from 5% by weight to 50% by weight and will preferably be in the 10% by weight to 30% by weight range.
The polybutenes which can be used in the compositions according to the invention are polybutene oligomers having a molecular weight in the range of from 700 to 2500 Daltons with the preferred polybutene having a molecular weight in the range of from 1000 to 1500 Daltons. The amount of polybutene which can be used in the compositions according to the invention can range from 1% by weight to 70% by weight and will preferably be in the 20% by weight to 60% by weight range.
The antioxidants which can be used in the compositions according to the invention are substituted diarylamines, phenothiazines, hindered phenols, or the like. Preferred antioxidants include thiodiethylene bis-(3,5-di-tert-butyl-4-hydroxy) hydrocinnamate, available commercially as Irganox(copyright) L 115, a trademark product of Ciba-Geigy and a mixture of dioctyl- and dibutyldiphenylamines, available commercially as Irganox(copyright) L 57, a trademark product of Ciba-Geigy and combinations of thiodiethylene bis-(3,5-di-tert-butyl-4-hydroxy) hydrocinnamate and a mixture of dioctyl- and dibutyldiphenylamines. The amount of antioxidant which can be used in the compositions according to the invention can range from 0.05% by weight to 1.0% by weight and will preferably be in the 0.2% by weight to 0.8% by weight range.
The extreme pressure additive which can be used in the compositions according to the invention are thermally stable, sulfur/phosphorus type EP additives such as Lubrizol(copyright) 5045 industrial gear oil additive and the like. A typical EP additive will have the following physical properties: (1) specific gravity @ 15.6xc2x0 C. equal to 1.022; (2) viscosity in centistokes @ 100xc2x0 C. equal to 14.3; (3) color, ASTM D 1500 equal to 4.0; (5) % boron by weight equal to 0.36; (6) % nitrogen by weight equal to 1.21; (7) % phosphorus by weight equal to 1.61; (8) % sulfur by weight equal to 19.6. The amount of extreme pressure additive which can be used in the compositions according to the invention can range from 1% by weight to 3% by weight and will preferably be in the 1.5% by weight to 2.5% by weight range.
The lubricant compositions according to the invention are typically made by thoroughly mixing all the components together with the aid of conventional mixing equipment while supplying such heating as necessary to maintain fluidity of the mixture.
The following examples are meant to illustrate but not limit the invention.